1. Field of the Invention
The present invention relates to an apparatus and method for controlling driving of a light-source device, and more particularly, to an apparatus and method for controlling driving of a recording head used for forming a permanent visual image on a recording medium according to an electrophotographic method.
2. Description of the Related Art
Conventionally, when forming a permanent visual image on a recording medium according to an electrophotographic method, it is necessary to form a latent image by projecting light emitted from a light-source device onto a photosensitive member.
For that purpose, recording heads, each including, for example, an LED (light-emitting diode) array, particularly, a self-scanning LED array (hereinafter termed a "SLED"), have been known.
A SLED head, serving as a recording head having SLED chips arranged in the form of an array, outputs an amount of light necessary for exposing a photosensitive member of an image forming apparatus by emission of light-emitting thyristors. Conventionally, when using four SLED heads arranged in parallel as an exposure light source of a four-drum-tandem-type color printer, and, for example, forming an image only by one (for example, the K station) of Y (yellow), M (magenta), C (cyan), and K (black) stations (image forming units) depending on image data, only a SLED head necessary for exposure of the photosensitive member is driven and lit while stopping the operations of the SLED heads of other stations.
However, when only the SLED head of one station is driven in order to emit light from the light-emitting thyristors of that head, the temperature of the SLED head gradually increases, causing a decrease in the amount of light. That is, a difference in the amount of light is produced between a SLED head which is continuously lit and a SLED head for which driving has just started, due to a difference in the temperature.
If a full-color image is output (i.e., by emitting light from all of the SLED heads of the four stations) after the above-described case of using only the K station, a deviation occurs in color balance and a sharp image cannot be formed, because the amount of exposure by heads which have not been driven is larger than that of the head which has been driven.